Composite ink jet printhead and relative manufacturing process

ABSTRACT

The composite printhead ( 1 ) is made up of an active module ( 7 ), consisting of a thin plate ( 8 ) of silicon, on which a plurality of chambers ( 14 ) is produced, housing corresponding heating resistors ( 10 ), electrically connected through an interconnection network to corresponding external contact pads ( 37, 42 ), and of a support element ( 3 ) for the active module, in turn consisting of a portion of plate ( 22 ) of a rigid, insulating material, provided with an elongated slot shape, ink feeding duct ( 5 ), traversing the thickness of the support element ( 3 ). The active module ( 7 ) is built separately from the support element ( 3 ) and later mounted integrally upon the support element ( 3 ). Also mounted later to the support ( 3 ) is a frame ( 16 ) surrounding the active module ( 7 ) to provide hydraulic sealing. Finally the module ( 7 ) and the frame ( 16 ) are covered with a metallic or resin lamina ( 17 ), bearing an array of nozzles ( 18 ) aligned with and facing the ejection chambers ( 14 ).

TECHNICAL FIELD

This invention relates to a composite ink jet printhead and to theprinthead manufacturing process, particularly for a “top-shooter” typeink jet printhead, i.e. the type in which the droplets of ink areejected perpendicularly to the substrate containing the heating elementsand the ejection chambers.

BRIEF DESCRIPTION OF THE STATE OF THE ART

As is known in the art, for instance from the Italian patent No. 1234800and from the U.S. Pat. No. 5,387,314, printheads of the type mentionedabove are made using as the support a thin wafer of crystalline siliconapprox. 0.6 mm. thick and with a diameter of approx. 150 mm., from whichthe single heads will be separated after they have been manufactured,while a plurality of overlapping layers is deposited on the silicon discwith known vacuum processes. Produced on these layers are the NMOSactive devices for each head, made using integrated circuit technology,the heating elements, or resistors, and the relative electricalconnections to the outside, protected and separated by correspondingisolating layers; the resistors are housed inside chambers built intothe thickness of a further overlapping layer of photosensitive material,for example VACREL™, and obtained in a photolithographic processtogether with the lateral ink feeding channels; the channels of thechambers communicate with a narrow, oblong ink feeding duct, in theshape of a slot, which crosses through the silicon support and thelayers already deposited and is arranged between two parallel rows ofchambers, disposed on both long sides of the slots.

Before being separated, each of the heads still on the wafer has ametallic or plastic lamina, bearing the ejection nozzles, applied to itand attached by gluing on top of the layer of the chambers, andpositioned precisely so that each nozzle coincides with a correspondingchamber.

The wafer thus completed is cut according to a rectangular mesh grid toseparate the single heads, each of which is completed by being connectedto a flat cable, the ends of which are soldered to corresponding contactpads made along an edge of each single head and connected by way ofinternal connections to the resistors.

In the current art, machining of the slots is performed after the activesemiconductor devices have been made, and the layers of the resistors,the layer of the relative electrical connections and the protectionlayers above have been deposited on the silicon wafer. The two-stepmachining work starts on the surface opposite that bearing the resistorswith a partial sand-blasting process, or chemical etching process on thesilicon wafer and is completed with an erosion performed by sandblasting, or with a laser beam. Alternatively the slots can be made in asingle, total sand blasting operation.

Machining of the slots in the ways mentioned above often results ingeometrical irregularities, or an offsetting of the edge of the slotswith respect to the resistors, or even damage to the layers that arecrossed through, on account of splintering on the edge of the slotfacing the chambers, with a resultant high level of production rejects,specially for slots that are long (>½″) and narrow (<250 μm), inaddition to being a lengthy, complex and expensive process.

SUMMARY DESCRIPTION OF THE INVENTION

The main object of this invention consists in producing printheadswithout the drawbacks mentioned above and in particular in producing theprintheads in lesser time and at lower cost with respect to the knownart, and in which the machining of the ink feeding ducts (slots) doesnot interfere with the integrity of the layers in the area of theresistors and of the ejection chambers and channels leading to thechambers.

A further object of the invention consists in manufacturing ink jetprintheads in which the extent of the surface of the silicon wafer usedby the printhead is reduced to the minimum.

A further object of the invention is that of defining an innovativeprocess for manufacturing ink jet printheads, in which machining of theink feeding ducts does not interfere with the integrity of the resistorsand of the relative protective layers and in which each head is madeusing a silicon wafer of very low dimensions, to increase the printheadproduction yield and permit the production of multiple colour heads,namely with various independent groups of nozzles, capable of ejectingvery small droplets (<5 pl), particularly suitable for the printing ofimages of photographic resolution.

In accordance with the predefined objects, according to this invention,a composite, ink jet printhead and innovative head manufacturing processare presented, characterized in the way defined in the correspondingmain claims.

This and other characteristics of the invention will appear more clearlyfrom the following description of a preferred embodiment of theprinthead and of its manufacturing process, provided by way ofnon-restrictive example, with reference to the figures of theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents an expanded perspective view of a composite, ink jetprinthead, made according to this invention;

FIG. 2 represents a partially sectioned plan view of the printhead ofFIG. 1;

FIG. 3 is a section according to the line III-III in FIG. 2;

FIG. 4 represents the disposition of the support elements, or bases, ona support plate before they are cut and separated;

FIGS. 5 and 6 illustrate disposition of the contact pads on two activemodules of different types;

FIGS. 7 and 8 represent two different techniques for soldering the atcable to the contact pads of an active module;

Figures from 9 to 13 represent different geometries of composite ink jetprintheads, according to the invention;

FIG. 14 represents the wiring diagram of an addressing circuit,integrated in an active module, according to the invention; and

FIG. 15 schematically represents the disposition of the circuit of FIG.14 on an active module.

DETAILED DESCRIPTION OF THE INVENTION

The fundamental idea, at the basis of the solution provided by thisinvention, is that of making an ink jet printhead 1 (FIG. 1),substantially comprising two parts machined separately and assembledtogether only at the end of the respective machining processes; more inparticular the new composite printhead is made up of a first supportelement, or base 3, of a rigid and isolating material; a slot-shapedaperture 5 is made on the base 3, going right through the thickness ofthe base itself. This aperture constitutes the ink feeding duct, as willbe described in detail later.

A second element, called active module 7, consists of a plate ofcrystalline silicon 8, upon which, with processes known in the art andseparately from the base 3, the NMOS active devices are made. Theseconstitute the driving and selecting circuits 12. Layers are thendeposited of heating elements, or resistors 10, and of relativeinterconnections, followed by a photosensitive resin film 15, in whichthe ink ejection chambers 14, aligned with the corresponding resistors10, are made.

At this point, each active module 7 is fastened on a pre-preparedcorresponding base 3, by means of gluing and pressing. Subsequently aframe 16 of resin having the same thickness as the module 7 andsurrounding the module, is glued on the base 3 to improve hydraulicsealing.

Finally each active module 7 is completed with the application on thephotosensitive film 15 and partially above the frame 16, of a metallicor plastic lamina 17 bearing the ejection nozzles 18, disposed withprecision in correspondence with the chambers 14 and facing therespective resistors 10, in such a way that the ink droplets are ejectedin a direction perpendicular to the plane of extension of the resistors10 (top shooter).

A more detailed description will follow of the structure and themanufacturing process of a non-restrictive, preferred embodiment of acomposite printhead, according to the invention, and in particular of ahead with a single line of nozzles.

It remains understood that the solution idea set forth in this inventionis also applicable to so-called multiple heads, having more than oneactive module and different geometries.

Preparation of the Base 3

The head 1, as already anticipated with reference to FIG. 1, comprises asupport element, or base 3, substantially rectangular in shape, ofthickness between 400 and 600 μm and delimited by two flat and parallelopposite surfaces 20 and 21; the base 3 is cut from a plate 22 (FIG. 4)of rigid, electrically isolating, chemically inert material, withcoefficient of thermal dilatation close to that of the crystallinesilicon. Among the materials that may be used to produce the base 3, byway of non-restrictive examples, the following may be quoted: alumina,borosilicate glass, resin, or even crystalline silicon, not necessarilyof prime purity and surface finishing.

As an example, the choice for use in production of the bases 3 falls ona plate 22 (FIG. 4) of ordinary, commercial type silicon, without anyparticular electrical and mechanical characteristics, having diameterapprox. 150 mm. and thickness approx. 400-600 μm, from whichapproximately 500 unitary bases may be obtained after machining,assuming that each base has dimensions of approx. 5×14 mm.

The preparation of the bases 3 proceeds according to the following steps(FIG. 4).

Step 1) on a face 20 of the plate 22, a metallic film 24, for example Alor Cr, of thickness 1000-3000 A°, is deposited, and on this is applied alayer of photosensitive material (photoresist) 26, in turn exposed witha mask for defining the following positioning references:

1a) reference and alignment marks 29, for high precision positioning,that is to say with a tolerance of +/−1 μm of the active module 7 on itsbase 3;

1b) outline 30 of the slot 5;

1c) separation lines 32, along which the single support bases 3 willsubsequently be cut;

1d) outlines of areas 33 of dispensation of the adhesives, for gluingthe active module 7 on the base 3;

1e) outline of the area of dispensation 34 of the adhesive for gluingthe resin frame 16, which laterally seals the module 7 on its base 3.

Step 2) exposure of the photoresist 26 to a light source through a maskand subsequent development; removal of the superfluous portions of themetallic film 24, not protected by the mask used.

Step 3) deposition of an “adhesion promotion” type film to facilitateadhesion of the glues.

Step 4) etching of the slot 5, without particular restrictions ofprecision, since there are no delicate components, such as resistors, orNMOS circuits on the base 3. The etching may be performed with one ofmethods known in the art, such as sand blasting, laser beam, vacuumplasma, anisotropic chemical etching, etc. Where alumina, or ceramic, isused, the slot is obtained by pressing before to baking.

Production of the slots 5 concludes preparation of the bases 3, whichare provisionally deposited in a temporary store.

Preparation of the Active Modules 7.

To produce the active modules 7 a crystalline silicon disc or wafer isused. Not depicted in any of the drawings, the wafer is between 400 and600 μm thick; initially, both the outer, opposite surfaces arepassivated with an isolating layer of silicon oxide, SiO₂; supposingthat each active module 7 has plan dimensions of 10.5 mm×1.6 mm, roughly700 silicon wafers may be made, without considering the inevitableproduction rejects.

Then on one of the passivated surfaces, using the known semiconductortechnologies, for each active module 7, the NMOS circuits for drivingthe resistors 10, the logic circuits for selecting are made, and theresistors 10, the protective layers, the internal interconnections andthe external contact pads are produced with a deposition of conducting,isolating and resistive layers; finally a layer of photosensitivepolymer is laminated, in which, following exposure and development, theink ejection chambers are built, according to the manufacturingprocesses known in the art, for instance as described in detail in theabove-mentioned Italian patent No. 1.234.800, or in the Italian patentapplication No. TO 2001 A001019 filed in the name of the applicant,which are recalled for reference.

Following the preparation process described, according to the invention,at least two types of active modules may be produced by way ofnon-restrictive example:

a first type called “Module A” (FIG. 5), in which the driving circuit12, integrated in the module, is laid out as an NMOS matrix, whichrequires a large number of external connections, or contact pads 37,arranged on the long side 38 opposite the resistors 10;

a second type called “Module B” (FIG. 6) which, as well as the drivingcircuit 12, also integrates on board the CMOS or NMOS selection logic40, with a further reduction in the number of contact pads 42 forexternal connection, which can be disposed on the short sides 43 of themodule 7.

Once construction of all the active modules contained in the silicondisc has been completed, after the customary sight and electrical testinspections, the single modules are separated by cutting of the discaccording to a rectangular grid of dimensions in line with thedimensions of the single modules.

Production of the Composite Printhead

Composition of the printhead according to the invention is completedwith an operation of mounting of each of the active modules 7 on each ofthe bases 3 still joined on the plate 22, and is conducted in thefollowing steps:

step 5) dispensation of an polymerizable adhesive in the areas 33 wherethe active modules 7 will be mounted on the plate 22;

step 6) positioning and alignment of the active modules with precisionof +/−1 μm on the bases 3 of the plate 22, taking reference between themarks 29 of the base 3 and corresponding marks 29′ made on each module7;

step 7) application on the bases 3 of spots of UV ray hardened bonder tokeep the single active modules in place during the subsequent phase ofpolymerization of the polymerizable adhesive;

step 8) polymerization of the polymerizable adhesive after completingthe positioning and alignment of the individual active modules in therelative positions on the plate 22;

step 9) dispensation of adhesive in the areas 34 where the frames 16 arebonded;

step 10) assembly of the resin frames 16 on the bases 3, according tothe references of the separation lines 32 of the plate 22; the frames 16are made from a substantially rectangular shaped resin plate (FIG. 1),having a central aperture 16 a, also rectangular in shape, complementaryto the dimensions of the active module 7 and suitable for surroundingthe active module 7, in contact with at least three contiguous sides“a”, “b”, “c” of the active module 7 (FIGS. 2, 3); the frame 16 is keptat a distance from the fourth side “d” of the active module 7, that isto say the fourth side “e” of the aperture 16 a is disposed beyond theslot 5 with respect to the fourth side “d” of the active module 7,provided with chambers 14, so as to constitute an ink store chamber 5 a,in communication both with the feeding slot 5 and with the ejectionchambers 14; the frames 16 must be of the same thickness as the activemodules 7 in order to form together with the active module 7, a uniformsurface, that facilitates subsequent bonding of the nozzle-bearinglamina 17 (FIG. 1);

step 11) polymerization of the adhesive in order to block the frames onthe plate 22;

step 12) application of an adhesive on the upper surface of the frames16, for subsequent mounting of the laminas 17 bearing the ink-ejectingnozzles; the nozzle-bearing laminas 17 adhere to the layer 15 ofphotopolymer by thermal effect; alternatively a film of thermoplastic,or thermohardening material may be applied on the frame, deposited bytampography, rolling, silk screen printing, or more simply through alayer of semi-liquid bonding agent, dispensed flat in a groove, notrepresented in the drawings, prepared in the frames;

step 13) assembly of the nozzle-bearing lamina 17 and its temporaryalignment with respect to the resistors 10 and fastening of said laminawith a number of spots of bonding agent 19, 86 (FIGS. 1, 13), beforeseparation of the portion of nozzle-bearing lamina, relative to eachsingle module, from the bearing reel, not depicted in the drawings, inthe case of plastic laminas, or from the pre-engraved sheet, in the caseof metallic laminas;

step 14) pressing at controlled temperature and duration of all thelaminas 17 of all the active modules 7 assembled on the plate 22, forgluing of the laminas on the layer of photosensitive polymer 15 of eachof the active modules 7 and on the frames 16; at the end of thisoperation, the nozzle-bearing laminas 17 constitute an upper closingwall of both the ejection chambers 14, and of the store chambers 5 a,communicating with the slots 5;

step 15) cutting of the plate 22 along the separation lines 32 toproduce the individual composite printheads.

The composite heads thus produced have a flat cable 45 connected tothem, through the soldering of its ends to the contact pads 37, 42, madeon the edges of each active module 7; the soldering may be performedwith the standard process, known in the sector art, called “TapeAutomatic Bonding” or T.A.B. (FIG. 7), or with thermoplastic adhesivesof the A.C.F. (Anisotropic Conductive Film) or A.C.P. (AnisotropicConductive Paste) type (FIG. 8), made from a thermoplastic film 44, orrespectively a paste resin to be dispensed, including small electricallyconductive balls, dispersed through the polymer; the Tin-Bismuth alloybased conducting balls, with melting point approx. 140° C., produce anoptimal electrical contact between the flat cable 45 and the contactpads 37, 42 of the modules 7, such as for instance the commerciallyknown product Loctite ACP 3445™.

The A.C.F. or A.C.P. technique comes with the advantage that the contactconductors 46 of the flat cable 45 (FIG. 8) are borne by the same flatcable, with the advantage that the header edge 47 of the flat cable maybe placed very close to the edge 48 of the nozzle-bearing lamina 17 andthe thickness of the flat cable can be chosen so that the upper surface49 of the flat cable is on the same level as that 49′ of thenozzle-bearing lamina 17; conversely, with T.A.B. (FIG. 7), thesoldering ends 50 of the flat cable are arranged embossed, creating acavity 52 which can be filled with a protective UV resin 53.

The A.C.F. or A.C.P. type connection is feasible with high definitionheads; in fact, the ejected ink droplets may drop in volume to about 4-6pl., with energies in play of 1-2 μJ, so that the electrical currentstraversing the contact pads are in the order of 100 mA, or less.

The low level of consumed current means that the area occupied by theNMOS driving circuits (FIGS. 5, 6) may be reduced, with the resultantpossibility of reducing the width “W” of the active module 7; this alsoallows the number of nozzles aligned in a single line to be increasedinside a vast range, increasing the height “H” of the active module 7.

With a step of 1/300″ between the resistors, that is to say between thenozzles, a module of height “H” up to 1″ may be built, withoutencountering the problems of manufacturing the ink feeding slots 5, asthese are made apart on the support plate 22.

The printhead preparation process described above is also suitable,without any particular amendments, for the preparation of multipleprintheads, in which at least two, and possibly more active modules 7,are mounted on a single base, arranged in different configurations,according to the required level of printing performance.

Figures from 9 to 12 illustrate, by way of a non-restrictive example, anumber of possible configurations of multiple printheads, consisting ofa single base 55, on which a plurality of active modules 7, of type “A”,is mounted, in which the electrical connection pads are arranged on along side of each module 7, opposite the other long side, on which theejection chambers 14 are arranged; more particularly, FIG. 9 representsa printhead in which, on a single base 55, three active, “A” typemodules 7 for a colour printer are mounted.

The modules 7 are set one beside the other, in parallel in thehorizontal direction, i.e. parallel to the printing direction, indicatedby the arrow “F”, and with a pitch of the nozzles that gives a printresolution of 300, or 600 D.P.I.; designated with the numeral 60 is theouter edge of the support base 55, numeral 61 is that of the frame 16 ontop, 62 the three nozzle-bearing laminas, designated with 63 are thethree, different colour ink feeding slots; designated with 63 a are theink chambers, similar to those designated 5 a in FIG. 3, delimited bythe lamina 62, by the sides “e” of the aperture 16° and by the side “d”of the active modules 7.

The numeral 64 designates the nozzles aligned in the vicinity of thelong side “d” of each module 7, facing the corresponding slot 63, and 65the external connection pads to which the flat cable 66 is connected. Inthis version, the flat cable 66 is provided with three apertures 67 of awidth that does not cover the nozzle-bearing laminas 62; the contactends 68 of the flat cable 66 are disposed on a long internal side ofeach aperture 67.

FIG. 10 depicts a printhead with four active modules 7 set side by sidein two's, mounted on the same base 55, for printing with three coloursplus black; the four feeding slots 71, each suitable for supplying adifferent colour ink, are produced on the base 55, machined separatelyfrom the active modules 7, and the four active modules 7, adjacent andparallel to each slot 71, are then mounted on the base 70.

In the version of FIG. 10, two nozzle-bearing laminas 72, 73 are used,each of which bears two parallel rows of nozzles 18 and two modules sideby side.

The flat cable 45 is provided with a single rectangular aperture 75, andthe connection pads 76 are situated on the two long sides of theaperture 75.

FIG. 11 shows a monocolour head consisting of a single base 55 on whichare mounted two identical modules 7 aligned and touching head to head,with a pitch between the nozzles of 1/300″; this arrangement allowsnozzle pitch to be kept constant, even when two modules are straddled.In this way, by using two modules with height (H) ½″, a module of“equivalent” height 1″ is obtained, with which to perform printing witha resolution of 300 D.P.I. with a single pass, or of 600 D.P.I. in twopasses.

A single ink feeding slot 77 is made on the base 55. It is longer thanother similar ones because it has to feed two consecutive rows ofnozzles 18. Likewise the nozzle-bearing lamina 78 is made in a singlepiece and covers both the modules 7.

Finally, FIG. 12 illustrates a printhead made up of a single base 55,with three modules 7 aligned vertically, but each one separate from theother; this head may be used for printing in three colours at a pitch of1/300″, or 1/600″.

Again in FIGS. 11, 12, the flat cable 45 has a single aperture 75 andthe connection pads 76 are located on one of the long sides of theaperture 75.

Depicted in an exploded, perspective view in FIG. 13 is a multiple,three-colour printhead, with three “B” type modules 7 on a single base55, parallel and side by side in the direction of printing, indicated bythe arrow “F”. The base 55 is provided with three slots 80, in thevicinity of which the three active modules 7 are mounted.

A resin frame 81 of the same thickness as the modules 7 is glued on tothe base 55, in such a way as to partially surround each module andthereby improve hydraulic sealing. The frame 81 is provided withopposing protrusions 82, of dimensions suitable for insertion betweenthe modules 7, close to their ends 82, and for delimiting feedingchambers 83, communicating both with the corresponding slot 80 and withone of the groups of ejection chambers 14.

Glued to the frame 81 and to the three active modules 7 is a metallic orresin lamina 85, normally of Kapton™, provided with three parallel linesof nozzles 18. The nozzles 18 are set facing their correspondingresistors contained inside the chambers 14, so that the ink droplets areejected in a direction perpendicular to the surface of the resistorsthemselves; the lamina 85 also constitutes the upper closing wall of thechambers 83.

During assembly of the heads on the plate 22 (FIG. 4), the laminas 85are initially mounted on the frames 81 through a number of spots of UVbinder 86, to keep them stationary and integral with the frame 81,before being separated from the reel, not shown in the drawings, onwhich they are wound, in the case or plastic laminas, or separated froma larger, pre-engraved sheet, in the case of metallic laminas. Finallythe laminas 85 are glued by hot-pressing on the completed wafer.

The flat cable 45 has a single aperture 87, and the connection pads 88of the flat cable 45 are connected to corresponding pads 88′, made onthe edge of the short sides 89 of the modules 7. With this geometry,even more than three modules may be used, for example four modules(three colours plus black), with obvious advantages, e.g. thenozzle-bearing lamina 85 may be made of a single piece, the headoccupies less space on the horizontal, and the hydraulic sealing betweenthe modules 7 and with the environment is more secure.

The configuration of the head depicted in FIG. 13, in which the flatcable 45 is soldered by its head to the active modules 7, namely oncontact pads on the short sides 89 of the modules themselves, isrendered possible by the use of an addressing circuit operating in 3Dmode, with simple N-MOS active devices, and in particular of the typedescribed in the international patent application PCT/IT00/00271 withpriority Dec. 7, 1999 filed by Olivetti Lexikon S.p.A., and illustratedin part in FIG. 14.

For simplicity of presentation and by way of example, it is supposedthat each active module 7 of the head of FIG. 13 comprises 112 nozzles,to each of which corresponds a resistor R_(N) (N=1 . . . 112), in turnactivatable via a corresponding transistor T_(N); the resistors R_(N),and therefore the transistors T_(N), are laid out in 8 pairs of groups90 (FIG. 14) of seven resistors R₁, R₂, . . . R₇ each; the resistors R₁,R₂, . . . R₇ of each group 90 are connected between the “drain” D ofeach corresponding transistor T₁, T₂, . . . T₇ and in common to eachprimitive line P_(M) (M=1 . . . 8); the transistors T₁, T₂, . . . T₇ ofeach group 90 have their “source” connected in common to the “drain” ofa selector transistor 91, 91 a, while each of their “gate” terminals isconnected to one of the seven address lines A_(A) (A=1 . . . 7); in turnthe selector transistors 91, 91 a have their “source” connected to acommon ground terminal 92. The selector transistors 91 belonging to eachfirst group and the selector transistors 91 a belonging to each secondgroup of each pair have their “gate” terminal connected to one or theother of two selection enabling lines, SW1 and SW2 respectively.

Therefore, with the pre-settings selected for the example describedabove, in which the number of primitives P=8, the number of addressesper primitive is A=7 and the number of selections SW=2, the followingare required:

8 (P)+7 (A)+2 (SW)+2 (ground)=19 external contacts (pads) 88′ for eachactive module 7, which is therefore provided with:

8 (P)*7 (A)*2 (SW)=112 resistors R_(N), that is to say 112 ejectionnozzles 18 (FIG. 13).

FIG. 15 represents schematically an active module 7, built according tothe pre-settings of the example presented. The plan dimensions of theactive module 7 are length 10.5 mm and width 1.6 mm, i.e. the dimensionof the short side 94.

The 19 pads 88′ are subdivided (+one for back-up) ten per side 94,spaced apart by 20 μm, each pad having width 140 μm.

The circuit of FIG. 14 is represented schematically on the active module7 of FIG. 15 in the following way:

the staggered lines 95 represent the sixteen groups of resistors R_(N),each pair of groups being connected to a primitive line (P_(M));

the squares 96 with vertical lines represent the transistors T_(N)corresponding to each group of resistors R_(N), which receive theaddress signals A_(A) from an array 97 of conductors, which alsoincludes two conductors for the pulses SW, which go to drive theselection transistors 91, represented by strike-through rectangles 98,below which runs a large ground return conductor 99.

The pads 88′ on the short side 94′ (on the left in FIG. 15) aretherefore connected to the following conductors:

P1, P2, P3, P4; A1, A2, A3, A4; GRN;

whereas the pads 88′ on the short side 94 (on the right in FIG. 15), areconnected to the conductors:

P5, P6, P7, P8; A4, A5, A6, A7; SW1, SW2;

It is clear from the description that the composite printheads, producedaccording to the invention, have numerous advantages with respect to theheads of the prior art. Their construction is in fact simpler because,as the ink feeding slots are built separately, they do not have any ofthe precision and high quality finishing constraints required by thetraditional construction techniques. Furthermore the new heads are alsoless expensive because the active modules may be built of lesserdimensions than in the previous techniques, saving considerablequantities of silicon and the noble metals used for the resistors andfor the internal interconnections, and also the labour required formanufacture of each single chip.

A further advantage obtained with the heads according to the inventionlies in the fact that, by using addressing circuits in 3D modeintegrated in the active modules, the number of external connections isgreatly reduced. This makes it possible to connect the conductors of theflat cable to contact pads, preferably arranged on the short sides ofthe active modules, so that a greater compacting can also be achieved ofmultiple printheads.

1. Ink jet printhead (1) of the type comprising: a plurality of nozzles(18) and a corresponding plurality of heating elements (10), suitablefor being selectively activated to produce the ejection of ink dropletsthrough said nozzles (18), said nozzles being disposed facing thecorresponding heating elements (10), the latter being housed inrespective chambers (14) suitable or containing ink, an active module(7) made up of a thin wafer (8) of silicon, bearing said plurality ofheating elements (10) and said respective chambers (14), said activemodule (7) being also provided along its sides (38; 43) with a pluralityof electrical contact pads (37; 42) connected to said heating elements(10) and suitable for being soldered to an array of feeding wires (45),a support element (3) for said active module (7), said support element(3) consisting of a portion of a plate (22) of rigid, isolatingmaterial, provided with a feeding duct (5) for said ink, traversing thethickness of said support element (3), wherein said active module (7) isbuilt separately from said support element (3) and subsequently mountedintegrally and placed on said support element (3) in such a way thatsaid chambers (14) are facing said feeding duct (5), a resin frame (16)mounted on said support element (3) and having the same thickness assaid active module (7), said resin frame (16) being provided with anaperture (16 a) of a shape substantially complementary to the dimensionsof said active module (7), suitable for accommodating said active module(7) and also said feeding duct (5) so at to define an ink store chamber(5 a) communicating with the ejection chambers (14) of said above module(7) and with the corresponding feeding duct (5), and a lamina (17)bearing said plurality nozzles (18), corresponding to said heatingelements (10) and to said chambers (14), said lamina (17) being mountedin part above said frame (16) and in part above said active module (7),but without covering the region of said electrical contact pads (37, 42)on said active module (7) so as to allow soldering of them to said arrayof feeding wires (45), said lamina (17) constituting also an upperclosing wall for said chambers (14) and for said communicating chamber(5 a).
 2. Printhead according to claim 1, wherein said feeding duct (5)is made in the form of a slot elongated in a longitudinal direction ofsaid active module (7).
 3. Printhead according to claim 1 or 2, whereinsaid aperture of said resin frame is suitable for accommodating saidactive module (7) in contact along at least three contiguous sides (a,b, c) of said aperture (16 a).
 4. Printhead according to claim 3,wherein said feeding duct (5) is arranged between a fourth side (d) ofsaid aperture (16 a) and the chambers (14) of the corresponding activemodule (7).
 5. Printhead according to any of the previous claims,characterized in that said active module (7) comprises integratedelectronic driving circuits, connected between said contact pads (37)and said heating elements (10), suitable for selectively activating saidhealing element (10), said contact pads (37) being arranged on a longside (38, b) of said active module (7), opposite said chambers (4). 6.Printhead according to any of the previous claims, characterized in thatsaid active module (7) comprises integrated electronic driving andselecting circuits, suitable for selectively activating said heatingelements (10) and connected between said contact pads (42) and saidheating elements (10), said contact pads (42) being arranged on bothshort sides (a, c, 43) of said active module.
 7. Multiple ink jetprinthead, of the type comprising: groups of nozzles (18) andcorresponding groups of heating elements (10), suitable for beingselectively activated to produce ejection of the ink droplets throughsaid groups of nozzles (18), the nozzles (18) of each group beingarranged facing the corresponding heating elements (10), the latterbeing accommodated in respective chambers (14) suitable for containingink, a plurality of active modules (7), each active module (7) beingmade of a thin silicon plate (7) bearing a corresponding group ofheating elements (10) and relative chambers (14), each of said activemodules (7) being also provided with a plurality of contact pads (37;42; 65) connected to said heating elements (10), a single supportelement (3; 55) for said plurality of active modules (7), said singlesupport element (3) being in turn made of a portion of a plate (22) ofrigid, isolating material and being provided with an ink feeding duct(5; 63; 71; 77) associated with each of said active modules (7), saidfeeding duct (5; 63; 71; 77) crossing through the thickness of saidsupport element (3; 55), wherein the active modules (7) of saidplurality are built separately from said single support element (3; 55),are subsequently integrally mounted on said single support element (3;55), and are positioned on it in such a way that the ejection chambers(14) of each active module (7) are facing the corresponding feeding duct(5; 63; 71; 77), a resin frame (16; 81) mounted on said single supportelement (3; 55) and having the same thickness as said active modules(7), said resin frame (16; 81) being provided with at least one aperture(16 a) having a substantially complementary shape to the dimensions ofsaid active modules (7) and being suitable for accommodating said activemodules (7) and the corresponding feeding duct (5), so as to define aplurality of ink store chambers (63 a), each communicating with theejection chambers (14) of a respective active module (7) and with thecorresponding feeding duct (5; 63; 71; 77); and a lamina (62, 72, 73;85), bearing groups of nozzles (18; 64) associated with said ejectionchambers (14), said lamina being mounted in part on top of at least oneof said active modules (7) and in part on top of said resin frame (16),but without covering the region of the contact pads (37, 42) on said atleast one of said active modules (7), said lamina constituting also anupper closing wall for the communicating chamber (63 a) and for theejection chambers (14), facing said communicating chamber (63 a),corresponding to said at least one of said active modules (7). 8.Multiple printhead according to claim 7, characterized by the fact thateach aperture (16 a) of said resin frame is suitable for accommodating acorresponding active module (7) in contact along at least threecontiguous sides (a, b, c) of said each aperture (16 a).
 9. Multipleprinthead according to claim 8, characterized in that said each aperture(16 a) of said resin frame accommodates, besides the correspondingactive module, also the corresponding feeding duct (5), arranged betweena fourth side (d) of said each aperture (16 a) and the chambers (14) ofthe corresponding active module (7).
 10. Multiple printhead according toany of the claims from 7 to 9, characterized in hat said plurality ofactive modules comprises three active modules (7) arranged side by sidein parallel, in the horizontal direction, i.e. parallel to the printingdirection (F), mounted on said single support element (55), the chambers(14) of each active module (7) facing a corresponding feeding duct (63)of said single support element (55).
 11. Multiple printhead according toany of the claims from 7 to 9, characterized in that said plurality ofactive modules comprises four active modules (7) arranged side by sidein two's, mounted on said single support element (55), for printing inthree colours plus black, the chambers (14) of each active module (7)facing a corresponding feeding duct (71) of said support element (55).12. Multiple monocolour printhead according to any of the claims from 7to 9, characterized in that said plurality of active modules comprisestwo identical active modules (7) aligned and touching head to head,mounted on said single support element (55), for printing in a singlecolour, said support element (65) comprising a single feeding duct (77),extending in a position facing the chambers (14) of both of said twoactive modules (7), the chambers (14) of said two active modules (7)being separated by a constant step, said resin frame (16) being providedwith an aperture (6 a) suitable for accommodating both said two activemodules (7) and said nozzle-bearing lamina (78) being sized so as tocover both of said two active modules (7).
 13. Multiple printheadaccording to any of the claims from 10 to 12, characterized in that eachactive module (7) of said plurality comprises a group of pads (66)arranged on a long side of said active modules (7), opposite saidchambers (14).
 14. Multiple printhead according to claim 13,characterized in that each active module (7) of said plurality comprisesintegrated electronic driving circuits (12), suitable for selectivelyactivating said heating elements (10) and connected between said groupsof pads (65) and said heating elements (10).
 15. Multiple printheadaccording to any of the claims from 7 to 9, characterized in that saidplurality of active modules comprises at least three active modules (7)arranged side by side in parallel, in a direction parallel to theprinting direction (F), mounted on said single support element (55), thechambers (14) of each active module (7) facing a corresponding feedingduct (80) of said support element (55), each active module (7) of saidplurality comprising integrated electronic driving circuits (12) andintegrated CMOS or NMOS logic selecting circuits (40), suitable forselectively activating a plurality of groups of heating elements (10,R_(N)) and connected between groups of pads (42, 88′) and said heatingelements (10, R_(N)), said pads (42, 88′) being arranged on shortopposite sides (43, 89) of each active module (7).
 16. Multipleprinthead according to claim 15, characterized in that said CMOS or NMOSlogic selecting circuits (40) comprise a 3D mode addressing circuit, forselectively activating said heating elements (10, R_(N)), saidaddressing circuit comprising selection transistors (91, 91 a)associated with each of said groups of heating elements (10, R_(N)),suitable for activating in sequence predetermined heating elements (10,R_(N)), in each of said groups, defined by a pre-established combinationbetween a selection address (A_(A)) and a logic primitive signal(P_(M)), said selection transistors (91, 91 a) being enabled by a logicenabling signal (SW1, SW2).
 17. Process for producing an ink jetprinthead of the type comprising a plurality of nozzles (18) and acorresponding plurality of heating elements (10), suitable for beingselectively activated to produce the expulsion of ink droplets throughsaid nozzles (18), said nozzles (18) being arranged facing correspondingheating elements (10), the latter being accommodated in respectivechambers (14) suitable for containing ink, said process comprising thefollowing steps: a) producing a plurality of active modules (7) each ofwhich is made of a thin silicon plate, bearing said plurality of heatingmeans (10) and said chambers (14); b) tracing on a surface (20) of aplate (22) of thin, rigid, electrically isolating material, of referencemarks (29), a grid of contour and separation lines (32) for delimiting aplurality of support elements (3) for said active modules, suitable forbeing cut from said plate; c) making on each of said support elements(3), delimited by said contour lines (32), at least one aperture (5),passing through the thickness of said support element; d) mounting oneach of said support elements at least one of said active Modules 7),with reference to said marks (29), in such a way that said plurality ofchambers (14) is facing each of said apertures (5); e) mounting on eachof said support elements (3) a resin frame (16), provided with at leastone aperture (16 a) of a shape complementary to the dimensions of eachof said active modules (7), suitable for accommodating correspondingactive module (7), and arranged adjacent to at least three contiguoussides of said active module (7) and sized for defining an ink chamberarranged between a fourth side (e) of said aperture and the chambers(14) of said active module (7); f) mounting on at least one of saidactive modules (7), or already mounted on the relative support element(3), of a lamina (17, 62, 72, 78) bearing a plurality of nozzles (18),corresponding to said plurality of chambers (14), in such a way that Didnozzles are facing corresponding heating elements (10); and g) cuttingsaid plate (22) according to said contour lines (32) for separating saidsupport elements (3) bearing at least one of said active modules (7),said frames (16) and a corresponding nozzle-bearing lamina (17 62, 72,78).
 18. Process according to claim 17, characterized in that step balso includes tracing on said surface (20) of said plate (22) thecontour (30) of said aperture (5) and the contours (33, 34) of areas ofdispensation of adhesive for mounting said active modules (7) on saidplate (22).
 19. Process according to claim 17, characterized in thatstep c also includes making said longitudinally elongated slot shapeapertures (5) of said active modules (7), following said traced contour(30).
 20. Process according to claim 17, characterized in that step d ispreceded by the operation of applying an adhesive inside said areasdispensation (30, 33).
 21. Process according to claim 17, characterizedin that step e is preceded by the operation of applying an adhesiveinside an area of dispensation (34) surrounding said active modules (7),for gluing said frame (16).
 22. Process according to claim 17,characterized in that step f also includes said lamina (17, 62, 72, 78)being positioned in part on top of said at least one active module (7),and in part on top of said frame (16), and the mounting being performedby pressing at a controlled temperature and for a controlled duration.